Aggression is the most serious and dangerous behaviour problem that dog owners may need to deal with. In order to treat the problem effectively, it is necessary to identify the type of aggression the dog displays. Some types of aggression include:

Since there are many different types of aggression, a trained animal behaviourist is the best person to make a diagnosis, determine the prognosis (including the chances of safe and effective correction) and develop an appropriate treatment regime. In some cases, a medical condition can be a contributing factor to aggression so prior to assessment by a behaviourist, we recommend a complete physical examination by a veterinarian, including blood tests to rule out organ dysfunction, if indicated.

Dominance or "Leader" Aggression

One of the most common types of aggression seen by veterinary behaviourists is dominance related aggression. In order to achieve security and cohesiveness within a group or pack, a hierarchy develops. Once a dog develops a position of leadership with a family member (or other dog), any challenge to that dog's leadership may lead to aggression. Dogs use facial expressions and body postures as signals to display dominance, such as standing tall, a high wagging tail, eye contact, or snarling. Aggression towards family members in one or more of the following circumstances along with dominant signaling may indicate dominance aggression; protecting resting areas or resources; restraint, pulling, pushing, discipline, punishment; staring, eye contact; handling by the owner; overprotection of a family member.

Fear Aggression

Fear aggression arises when a dog is exposed to people or other animals that the dog is unfamiliar with or those that have been previously associated with an unpleasant or fearful experience. Although some dogs may retreat when fearful, those that are on their own territory and those that are prevented from retreating because they are cornered or restrained, are more likely to fight. If the person or animal retreats, acts overly fearful or the pet is harmed or further frightened in any way (eg. a fight or punishment), the fear is likely to be further aggravated. Fear aggression towards family members might arise out of punishment or some other unpleasant experience associated with the owners. Many cases of fear aggression are seen as combinations or complicating factors of other forms of aggression (eg. dominance, maternal, possessive etc.) Fearful body postures in conjunction with aggression are diagnostic of fear aggression.

Play Aggression

Play aggression is commonly seen in young dogs that have not been taught appropriate bite inhibition. This can be directed towards people or other animals. Over-the-top excitement when playing, combined with nipping, biting or grabbing, are signs of play aggression. Although this is normal behaviour, it can lead to injury and other more serious forms of aggression as the dog matures. It needs to be handled correctly when the dog is young in order to prevent this.

Possessive Aggression

This type of aggression is often seen when people or other pets approach a dog that has an object that is highly desirable, such as a favourite toy, food or treat. While protecting possessions may be necessary if an animal is to survive and thrive in the wild, it is unacceptable when directed towards people or other pets in the household. What can be confusing for some owners is that it is not always food that brings out the most protective displays. Novel and highly desirable objects such as a tissue that has been stolen from a bin, a favoured toy, human food or a piece of rawhide are some of the items that dogs may try to protect aggressively.

Territorial or Protective Aggression

Territorial aggression is exhibited towards people or other animals that approach what the dog considers its property. This 'property' may be the dog's environment (such as the home or a favourite park) or it may be protective towards an owner or another pet. When a dog is protective of a person, this type of aggression may be exhibited wherever the dog is with that person, regardless of the location. Generally the target of this type of aggression is those people and animals that are least familiar to the dog. Territorial and protective aggression can be prevented with good, early socialisation of the dog as a puppy.

Predatory Aggression

Predation refers to the instinctive desire of dogs to chase prey animals. This type of aggression is characterised by stalking, chasing, attacking, and sometimes ingestion of the prey. This can sometimes be directed at people or other pets. Predatory aggression can often be strongest when the dog is running together with a group of dogs (pack mentality). This is a very dangerous form of aggression which must be prevented early on in a dog's development.

Pain-Induced Aggression

Pain-induced aggression is usually elicited by some form of handling or contact that elicits pain or discomfort. However, even if your dog is not exhibiting pain, certain medical conditions (endocrine imbalances, organ disease, etc) may make the pet more irritable and perhaps more prone to aggression. Fear and anxiety further compound many of these cases. Once your dog learns that aggression is successful at removing the stimulus, aggression may recur when similar situations arise in the future, whether or not the pain is still present.

Maternal Aggression

Maternal aggression is directed towards people or other animals that approach the bitch with her puppies. When bitches go through pseudo-pregnancy they may also become aggressive and begin to protect nursing areas or stuffed toys at the approximate time when the puppies would have been born. Once the puppies are weaned and the dog is speyed, the problem is unlikely to recur.

Redirected Aggression

Aggression that is directed towards a person or pet that did not initially evoke the aggression is classified as redirected. This is likely to occur when the dog is aroused and a person or other pet intervenes or approaches. Dogs that are highly aroused must be avoided. Since redirected aggression arises out of other forms of aggression, it is important to identify and treat the initial cause of aggression (eg. fear, territorial, etc) to prevent the problem.

Learned Aggression

Although learned aggression can refer to dogs that are intentionally trained to act aggressively on command (or in particular situations), learning is also an important component of most other types of aggression. Whenever a dog learns that aggression is successful at removing the stimulus, the behaviour is further reinforced. Some forms of aggression are inadvertently rewarded by owners who, in an attempt to calm the pet and reduce aggression, actually encourage the behaviour with patting or verbal reassurances. Pets that are threatened or punished for aggressive displays may even become more aggressive each time the situation recurs.

Other types of aggression

Aggression associated with medical disorders may arise at any age, may have a relatively sudden onset and may not fit into any canine species typical behaviour. Some medical conditions can, on their own, cause aggression, but in many cases a combination of behavioural factors and medical problems cause the pet to pass a certain threshold at which aggression is displayed. Infectious agents such as rabies, hormonal imbalances such as hypothyroidism, psychomotor epilepsy, hyperkinesis, neoplasia, and a variety of genetic and metabolic disorders can cause or predispose a dog to aggression. Painful conditions such as dental disease or arthritis, and medical conditions causing fever, fatigue or sensory loss might increase the pet's irritability.

In rare cases, aggression has no identifiable etiology and no particular stimuli that initiate aggressive displays. There may be a genetic propensity to aggression in some lines of some breeds but many of the cases previously labeled as "idiopathic," "rage" or "mental lapse aggression" have been disputed and in some cases subsequently reclassified. Only when there is no identifiable stimulus or cause for the behaviour, or when an abnormal ECG is documented, should the diagnosis of idiopathic aggression be considered.